1. Field
The present invention relates to a diffractive optical system.
2. Explanation of Related Art
Dioptric elements making use of refraction (lenses made principally of glass) are generally used in optical systems, in order to improve optical performance and, particularly, in order to restrain occurrence of aberration to improve imaging performance. In this case, in order to adequately suppress the Seidel's five aberrations and chromatic aberration at a reference spectral line, it is necessary to increase degrees of freedom of aberration correction and it is thus unavoidable to increase the number of lenses forming an optical system.
Particularly, in the case of an optical system used in a viewing optical system, an electronic viewfinder, or the like, the number of lenses forming the optical system tends to further increase when optical performance is attempted to improve. For achieving satisfactory correction for chromatic aberration of the optical system, it is necessary to use a plurality of optical materials with different refractive indices and dispersions and it is thus inevitable to use an optical material (glass) with a large specific gravity as well, which can readily cause increase in scale and weight of the optical system.